TomD8
Level 15

After you file

Except that filing the 2017 CA return may well cause a need to amend the taxpayer's federal return, if the taxpayer itemizes and deducts state income taxes.  Particularly since the deduction for state income taxes was not limited in 2017, as it was on 2018 returns.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.